1819.) Mr. Cooper on the Persulphates of Iron. 999 
colourless ; they do not at all indicate the presence of iron by 
the taste, which exactly resembles that of alum. They are 
very soluble in water, and contain a considerable quantity of 
that fluid combined, as will be shown in the sequel. They 
undergo the watery fusion ; and, when fused in their own water 
of crystallization, immediately change their colour and be- 
come red ; and if the whole of the water be driven off by heat, 
the dry mass is converted into two substances, one of which is 
soluble, but the other and greater portion insoluble in water : this 
latter, however, is readily taken up by the addition of muriatic acid. 
Three hundred and eighty grams of it were dried at a tempera- 
ture of about 300° Fahr. and lost 200 gr. of water: the whole, 
being redissolved by the addition of a small quantity of muriatic 
acid, the oxide of iron precipitated by ammonia, and the sulphuric 
acid by muriate of barytes, gave of 
Peroxide of iron. ........ PHB 7 ee tk Se 60 gr. 
Sulphate of barytes 352 gr. = sulphuric acid.. 120 
OS er GB Hee ua dnwniiinlt- > ih 200 
| 380 
This is the mean of three experiments ; and from these data, 
you will perceive the composition of this salt to be 
1 atom peroxide of iron 
+ 2 atoms sulphuric acid 
+ 15 atoms of water, or 
1 atom of peroxide of iron. .....-. eee eens oe AD 
2 atoms sulphuric acid ........-...scceeceees 80 
EO GLOMIS WALET us «2000 sve» v s'es.0 © o oun Serves 
considering hydrogen as unity, and oxygen 8. 
I feel confident of the existence of another salt of iron contain- 
ing a still larger quantity of acid; and I have little doubt 
that I shall be able to obtain it in a distinct form. If I should 
be successful, I shall send you the results; but hitherto I have 
obtained it only in very minute crystals, and which it is diffi- 
cult to free from the adhering excess of acid. The way in 
which I have formed this salt is as follows :—After separating two 
crops of crystals of the bipersulphate, 1 added sulphuric acid 
to the mother liquor, and evaporated till a pellicle formed on the 
surface: on cooling, the salt im question separated. These 
crystals appear, when very highly magnified, in the form of 
quadrangular plates. They are slightly deliquescent (but this 
probably may be owing to the adhering acid) ; they are perfectly 
white, and have a pearly lustre ; their taste isvery acid, but not 
so astringent as the former salt ; when caustic alkalies are added 
to them, they immediately indicate the presence of peroxide of 
iron. Owing to the above-mentioned circumstance of my hitherto 
not being able to get this substance in a form fit for analysis, I 
